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Next: <a href="Arithmetic-on-poly_005fints.html" accesskey="n" rel="next">Arithmetic on <code class="code">poly_int</code>s</a>, Previous: <a href="Consequences-of-using-poly_005fint.html" accesskey="p" rel="prev">Consequences of using <code class="code">poly_int</code></a>, Up: <a href="poly_005fint.html" accesskey="u" rel="up">Sizes and offsets as runtime invariants</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html" title="Index" rel="index">Index</a>]</p>
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<h3 class="section" id="Comparisons-involving-poly_005fint-1"><span>10.3 Comparisons involving <code class="code">poly_int</code><a class="copiable-link" href="#Comparisons-involving-poly_005fint-1"> &para;</a></span></h3>

<p>In general we need to compare sizes and offsets in two situations:
those in which the values need to be ordered, and those in which
the values can be unordered.  More loosely, the distinction is often
between values that have a definite link (usually because they refer to the
same underlying register or memory location) and values that have
no definite link.  An example of the former is the relationship between
the inner and outer sizes of a subreg, where we must know at compile time
whether the subreg is paradoxical, partial, or complete.  An example of
the latter is alias analysis: we might want to check whether two
arbitrary memory references overlap.
</p>
<p>Referring back to the examples in the previous section, it makes sense
to ask whether a memory reference of size &lsquo;<samp class="samp">3 + 4<var class="var">x</var></samp>&rsquo; overlaps
one of size &lsquo;<samp class="samp">1 + 5<var class="var">x</var></samp>&rsquo;, but it does not make sense to have a
subreg in which the outer mode has &lsquo;<samp class="samp">3 + 4<var class="var">x</var></samp>&rsquo; bytes and the
inner mode has &lsquo;<samp class="samp">1 + 5<var class="var">x</var></samp>&rsquo; bytes (or vice versa).  Such subregs
are always invalid and should trigger an internal compiler error
if formed.
</p>
<p>The underlying operators are the same in both cases, but the distinction
affects how they are used.
</p>

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<li><a href="Comparison-functions-for-poly_005fint.html" accesskey="1">Comparison functions for <code class="code">poly_int</code></a></li>
<li><a href="Properties-of-the-poly_005fint-comparisons.html" accesskey="2">Properties of the <code class="code">poly_int</code> comparisons</a></li>
<li><a href="Comparing-potentially_002dunordered-poly_005fints.html" accesskey="3">Comparing potentially-unordered <code class="code">poly_int</code>s</a></li>
<li><a href="Comparing-ordered-poly_005fints.html" accesskey="4">Comparing ordered <code class="code">poly_int</code>s</a></li>
<li><a href="Checking-for-a-poly_005fint-marker-value.html" accesskey="5">Checking for a <code class="code">poly_int</code> marker value</a></li>
<li><a href="Range-checks-on-poly_005fints.html" accesskey="6">Range checks on <code class="code">poly_int</code>s</a></li>
<li><a href="Sorting-poly_005fints.html" accesskey="7">Sorting <code class="code">poly_int</code>s</a></li>
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